The present invention relates to a fitting element for a fluidic device, in particular in a high performance liquid chromatography application.
In high performance liquid chromatography (HPLC), a liquid has to be provided usually at a very controlled flow rate (e.g. in the range of microliters to milliliters per minute) and at high pressure (typically 20-100 MPa, 200-1000 bar, and beyond up to currently 200 MPa, 2000 bar) at which compressibility of the liquid becomes noticeable. For liquid separation in an HPLC system, a mobile phase comprising a sample fluid with compounds to be separated is driven through a stationary phase (such as a chromatographic column), thus separating different compounds of the sample fluid which may then be identified.
The mobile phase, for example a solvent, is pumped under high pressure typically through a column of packing medium (also referred to as packing material), and the sample (e.g. a chemical or biological mixture) to be analyzed is injected into the column. As the sample passes through the column with the liquid, the different compounds, each one having a different affinity for the packing medium, move through the column at different speeds. Those compounds having greater affinity for the packing medium move more slowly through the column than those having less affinity, and this speed differential results in the compounds being separated from one another as they pass through the column.
The mobile phase with the separated compounds exits the column and passes through a detector, which identifies the molecules, for example by spectrophotometric absorbance measurements. A two-dimensional plot of the detector measurements against elution time or volume, known as a chromatogram, may be made, and from the chromatogram the compounds may be identified. For each compound, the chromatogram displays a separate curve or “peak”. Effective separation of the compounds by the column is advantageous because it provides for measurements yielding well defined peaks having sharp maxima inflection points and narrow base widths, allowing excellent resolution and reliable identification of the mixture constituents. Broad peaks, caused by poor column performance, so called “Internal Band Broadening” or poor system performance, so called “External Band Broadening” are undesirable as they may allow minor components of the mixture to be masked by major components and go unidentified.
An HPLC column typically comprises a stainless steel tube having a bore containing a packing medium comprising, for example, silane derivatized silica spheres having a diameter between 0.5 to 50 μm, or 1-10 μm or even 1-7 μm. The medium is packed under pressure in highly uniform layers which ensure a uniform flow of the transport liquid and the sample through the column to promote effective separation of the sample constituents. The packing medium is contained within the bore by porous plugs, known as “frits”, positioned at opposite ends of the tube. The porous frits allow the transport liquid and the chemical sample to pass while retaining the packing medium within the bore. After being filled, the column may be coupled or connected to other elements (like a control unit, a pump, containers including samples to be analyzed) by e.g. using fitting elements. Such fitting elements may contain porous parts such as screens or frit elements.
During operation, a flow of the mobile phase traverses the column filled with the stationary phase, and due to the physical interaction between the mobile phase and the stationary phase a separation of different compounds or components may be achieved. In case the mobile phase contains the sample fluid, the separation characteristics are usually adapted in order to separate compounds of such sample fluid. The term compound, as used herein, shall cover compounds which might comprise one or more different components. The stationary phase is subject to a mechanical force generated in particular by a hydraulic pump that pumps the mobile phase usually from an upstream connection of the column to a downstream connection of the column. As a result of flow, depending on the physical properties of the stationary phase and the mobile phase, a relatively high pressure occurs across the column.
Fittings for coupling different components, such as separation columns and conduits, of fluidic devices are commercially available and are offered, for instance, by the company Swagelok (see for instance http://www.swagelok.com). A typical tube fitting is disclosed in U.S. Pat. No. 5,074,599 A.
U.S. Pat. No. 6,494,500 discloses a self-adjusting high pressure liquid connector for use with high pressure liquid chromatography (HPLC) columns requiring liquid-tight and leak free seals between fittings and unions.
WO 2005/084337 discloses a coupling element comprising a male sealing element. The male sealing element may have a generally cylindrical shape, and defines a fluid passageway therethrough for the transmission of fluid. The male sealing element is secured to a ferrule which is located within a cavity of the nut. The coupling element also has a biasing element disposed between a retaining ring and the ferrule located within the nut cavity. This biasing element facilitates a fluid-tight, metal to metal (or metal to plastic, or plastic to plastic) seal between the male sealing element and female sealing element.
WO 2009/088663 A1 discloses liquid-chromatography conduit assemblies having high-pressure seals. A fluid-tight seal, proximal to the joint between two conduits, is provided, for example, through use of pressure, while a stabilizing seal, distal to the joint, is provided by adhering the conduits to the tube.
A high pressure connect fitting is disclosed at US 2008/0237112 A1. A tip of a seal contacts the walls of a tapered sealing cavity to form a primary seal. The volume of space between the very end of the tip and the end of a sealing cavity defines a dead space. As the seal is axially compressed within an annular recess, the tip engages the walls of the tapered sealing cavity to form the primary seal, and further deforms to occupy space otherwise associated with the dead space. As the tip of the seal engages the tapered sealing cavity, the end face of the seal compresses against the end of the annular recess to form a secondary seal extending radially around the tip of the seal.
U.S. Pat. No. 4,619,473 A describes a fluid passage connector for liquid chromatograph comprising a tube having a flat portion at one end and a seal seat surface. A similar device is known from the document “Viper Capillaries and Finger Tight Fitting System”, Dionex, http://www.dionex.com/en-us/webdocs/78632_DS-Viper-Capillaries-17Jul2009-LPN2283.pdf.
WO 2010/000324 A1, by the same applicant, discloses a fitting for coupling a tubing to another component of a fluidic device. The fitting comprises a male piece having a front ferrule and a back ferrule both being slidable on the tubing. The male piece has a first joint element configured slidably on the tubing. A female piece has a recess configured for accommodating the front ferrule and the tubing, and a second joint element configured to be joinable to the first joint element. The back ferrule is configured in such a manner that, upon joining the first joint element to the second joint element, the back ferrule exerts a pressing force on the front ferrule to provide a sealing between the front ferrule and the female piece, and the back ferrule exerts a grip force between the male piece and the tubing.
International Patent Application PCT/EP2009/067646 discloses a fitting element configured for providing a fluidic coupling to a fluidic device. An inlay is located in a cavity of a front side of a tubing. The inlay protrudes over the front side, at least before coupling of the tubing to the fluidic device. Upon coupling of the tubing to the fluidic device, the front side is fitted to the fluidic device for connecting a fluid path of the tubing to a fluid path of the fluidic device, and the inlay provides a sealing of the fluid path of the tubing and the fluidic device.
A bio-compatible column for use in liquid chromatography applications is known from U.S. Pat. No. 5,651,885 A.
Fittings made of PEEK material are known e.g. from http://webstore.idex hs.com/Products/specsheet.asp?vSpecSheet=257&vPart=F-301&vFrom=L, which however only allow limited pressure application below 300-400 bar.
Ni-coated PEEK-Capillaries are disclosed at http://www.vici.com/tube/ni-cladpeek.php.